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topic 24769

Removal of plasma sprayed tungsten carbide coatings?


A discussion started in 2003 but continuing through 2020

2003

Q. Removal of plasma sprayed tungsten carbide coatings: Does anyone have information on a process that would allow for the chemical stripping of tungsten carbide from ferrous and nonferrous metals without causing dimensional changes to the parent metal?

Ray Last
aerospace - Winnipeg, Manitoba, Canada


2003

A. There are chemical stripping methods. The right one depends on the powder you are using and the substrate. There is not any one solution that will do it all. The powder vendor should be able to give you some help with this.

One common non-proprietary formulation that will strip most thermal spray powders from steel is: Rochelle salt ~ 10 oz/gal, Soda Ash ~ 28 oz/gal. Strip part anodically at 6V. Of course, you would not want to try this on aluminum parts.

Jon Barrows
Jon Barrows, MSF, EHSSC
Springfield, Missouri



2003

? IS YOURS A TUNGSTEN CARBIDE COATING IN A COBALT MATRIX? IF SO, THE B-9 NICKEL STRIPPER FROM METALX, INC. IS BEING USED SUCCESSFULLY IN OTHER AEROSPACE FACILITIES.

Gayle Coffey
Metalx, Inc.
supporting advertiser
Lenoir, North Carolina
metalx banner


2003

A. Since Metalx has chimed in, I'll add that the B-929 formulation works for stripping cobalt bound tungsten carbide from aluminum parts. Theoretically, there are probably any number of nickel stripping solutions that will strip a tungsten carbide coating that uses cobalt as a binder.

Jon Barrows
Jon Barrows, MSF, EHSSC
Springfield, Missouri



April 26, 2012

Q. Jon

I have tried your procedure to strip tungsten carbide with this solution and it works very well!!

I had only one problem, I can't explain by myself that this solution doesn't attack steel parts and copper brazings. Can you explain this for me?

Thanks in advance,

Arjan

Arjan Cornet
Aerospace - Hoogerheide, Netherlands



What is the best pump for a Rochelle Salts stripping bath?

November 4, 2010

Q. We want to install a Rochelle salts bath. What is the best pump for agitation? Is it best to filter the solution?

David Fairbourn
Engineer - Sandy, Utah, USA


simultaneous November 5, 2010

A. That is going to depend on all of the tank makeup, temperature, flow rate desired, tank elevation, and things like filters needed/used.

James Watts
- Navarre, Florida


November 5, 2010

A. Assuming that you mean a stripping solution for thermal spray coatings and that you run at a middle-of-the-road temperature, a CPVC pump or a stainless pump would be fine and it can be either internal or external. And yes, you do want to filter it if you can. Filtration will extend the life of the solution considerably. The solid loading rate of the filter is quite high, so you want a bunch of surface area.

Jon Barrows
Jon Barrows, MSF, EHSSC
Springfield, Missouri




Analytical methods for Rochelle salt based HVOF stripping solution

February 14, 2012

Q. I am performing some tests to control the strip rate of solution used to strip tungsten carbide HVOF coatings. In the SAE specification, they are suggesting a solution made of sodium carbonate (150-225 g/L) and Rochelle salt (60-90 g/L) at a pH around 12. I would like to know if there are titration methods I could possibly use to control these concentrations.

Sylvain Bolduc
- Canada


February 16, 2012

A. Sure. Permanganate titration.

Tungsten compounds would likely precipitate upon acidification. Then, I imagine one would just titrate with KMnO4.

Look at the method for Rochelle's Salt in cyanide copper solutions.

dave wichern
Dave Wichern
Consultant - The Bronx, New York


February 22, 2012

Q. I am very sorry, but I'm not sure I'm following you here. Where does the tungsten come from? And if the tungsten come from an added compound, what compound is it better to use?

Sylvain Bolduc [returning]
- Montreal, Canada



Arc detection unit for electro chemical stripping

March 5, 2020

Q. Does anyone know of using an arc detection unit in electrolytic chemical stripping process tanks such as Rochelle salt. Any product and installation information would be appreciated.

Greg Widner
shop employee - Atlanta, Georgia

Metalx nickel stripper

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